The TARDIS takes the Doctor, Steven and Dodo to a space ark in the far
future, which is carrying humanity from the doomed Earth to their new
home, the planet Refusis. Dodo has a cold, however, for which the humans
and the subservient alien Monoids have no immunity. The Doctor must find a
cure for the common cold, and, centuries later, stop a revolution by the
Monoids brought about by the ramifications of the plague.

Production

Although it was writer Paul Erickson who formally received the commission
for The Ark on May 27th, 1965, the ideas for the story actually
originated with incoming producer John Wiles, who envisaged a Doctor
Who serial set on an enormous spaceship. Wiles discussed this image
with story editor Donald Tosh and Tosh involved Erickson, with whom he had
worked on Compact; Erickson's credits also included series such as
The Saint and several feature films. Tosh and Erickson developed
the storyline between them, from which Erickson then composed the
scripts.

The Ark was originally designated Serial Y. By early June, however,
it was known that the six-part Serial V would be expanded into the mammoth
twelve-episode The Daleks' Master Plan. To
account for the resulting rearrangement of the schedule for Doctor
Who's third season, The Ark would now be Serial X. Shortly
before the story entered production in January 1966, Erickson's agent
approached the BBC about amending the writing credit for The Ark to
list both Erickson and his wife, Lesley Scott. Copyright on the four
scripts, however, would remain solely with Erickson. This would be the
lone contribution to Doctor Who for both Erickson and Scott,
although Erickson did novelise the story for WH Allen prior to his death,
following a stroke, on October 27th, 1991.

The writing credit was amended to list both Paul Erickson
and his wife, Lesley Scott

Meanwhile, there had been considerable turmoil in the Doctor Who
production office during the months Erickson had been writing The
Ark. This had culminated in December with the resignations of both
Wiles and Tosh. Tosh was replaced by Gerry Davis beginning with the final
episode of The Massacre Of St Bartholomew's
Eve, the serial which preceded The Ark into production.
Some stability was introduced on February 15th, when Hartnell received a
contract extension to keep him on the show at least through Serial CC --
the last of the current production block. On the 24th, Purves' contract
was also renewed, but only with the understanding that his tenure on
Doctor Who would end after another twelve episodes, at the
conclusion of The Savages.

The director assigned to The Ark was Michael Imison, also working
on his only Doctor Who story. Imison had started at the BBC as a
story editor before becoming a director, with credits including
Compact. Production began on January 24th at the Ealing Television
Film Studios with the miniaturisation of the Guardian. A further four days
were spent at Ealing between January 31st and February 3rd. The first
three days concentrated on the Monoid battle on Refusis, while the final
day was used for the material in the Ark jungle. The latter involved the
use of a baby Indian elephant, named Monica, in addition to a variety of
other exotic animals. Bizarrely, Monica was forced to spent the previous
night in her van outside Imison's home after the van's driver had been
refused permission to park at Ealing.

It was around this time that Wiles' successor, Innes Lloyd, began
trailing the producer. Although Wiles would still be credited on The
Ark, Lloyd would have effectively replaced him by the end of
recording. Wiles, who had never been comfortable in the producer's chair,
returned to writing and directing. Most of his efforts were directed
toward the theatre, although he also earned credits on programmes like
Out Of The Unknown and Paul Temple (for which Erickson would
later write as well). Wiles had been ill for some time when he passed away
on April 5th, 1999.

Jackie Lane was asked to tone down the pronounced Cockney
accent she was employing for Dodo

The Steel Sky was recorded on February 18th in Riverside 1, the
studio home for the entire serial. Unfortunately, Imison vastly overspent
on this episode, meaning that savings would have to be made on the
following serial, The Celestial Toymaker. This
would be Jackie Lane's first full Doctor Who serial as Dodo after
the character debuted in the final episode of The
Massacre Of St Bartholomew's Eve. In the intervening week, Lane
had been asked to tone down the pronounced Cockney accent she was
employing for Dodo due to concern about a character not speaking proper
“BBC English”. This was challenging for Lane because
Erickson's scripts were written with Dodo's original speech pattern in
mind; nonetheless, her accent would all but disappear over the next few
recording sessions.

The Ark followed the usual Doctor Who production pattern
of taping each episode on successive Fridays, concluding with The
Bomb on March 11th. For this installment, Imison broke with the
typical Doctor Who recording scheme of taping scenes in story
order, the first time this had been attempted on such a large scale on
the programme. Nonetheless, it would prove to be a sign of the coming
changes to the way Doctor Who episodes were made.